1. Technical Field of the Invention
The present invention generally relates to the improvement of a transfer apparatus having a so-called frog-leg type transfer arm.
2. Description of the Related Art
For example, in the production of a semiconductor device, a transfer apparatus for transferring an object to be processed, e.g. a semiconductor wafer. As examples thereof, transfer apparatuss having a frog-leg type transfer arm are disclosed in Japanese Patent Laid-Open No. 4-129685 (the former) and Japanese Patent Laid-Open No. 6-15592 (the latter).
The transfer apparatus disclosed in the former publication comprises a transfer arm which comprises: a pair of small rotating shafts comprising two parallel shafts which are provided on a large rotating shaft at an interval and which simultaneously rotate in different directions; first arms, one end portions of which are fixed to the pair of small rotating shafts; second arms, one end portions of which are connected to the other end portions of the first arms by means of a pin; and a pick for holding a wafer, the pick being connected to the other end portions of the second arms by means of a pin. In addition, the other end portions of the first arms are connected to one end portions of third arms, which are directed in the opposite direction to the second arms, by means of a pin, and the other end portions of the thirds arm are connected to the pick by means of a pin.
The transfer apparatus disclosed in the latter publication comprises: a central hub; a pair of arms which are arranged so as to rotate coaxially with the hub; two picks which are spaced from each other by 180 degrees; a joint linkage for connecting each of the picks to one end portion of a corresponding one of the arms; and a drive unit for rotating the arms in opposite directions to extend one or the other of picks from the central hub in a radial direction and for rotating the arms in the same direction to coaxially rotate the picks. This transfer apparatus is provided in, e.g., the central portion of a transfer chamber, and is designed to move and transfer a wafer to a processing chamber, a load-lock chamber and so forth, which are arranged around the transfer chamber, by combining the rotation of the transfer arm while being contracted with the elongation and contraction of the transfer arm.
However, both of the above described transfer apparatuss can not sufficiently increase the length of the transfer arm when it is extended, considering the size of the transfer arm when it is contracted. In other words, if the length of each arm is increased in order to increase the length of the transfer arm when it is extended, the size of the transfer arm when it is contracted is increased, so that there is a problem in that the size of the transfer chamber for rotatably housing the transfer arm in its contracted state is unavoidably increased.